Robin,
when i had my R200SS i found collimation a problem. it too is a fast f ratio.
Looking at this link you can see things are not just centred but they also have to be orthagonal and aligned not sure if you can glean something from this? i do conceed that there is still an alignment problem rather than just the secondary and the focuser. you may have to shim the primary mirror as well as the spider to get it centered in the focuser?